Many compounds having a basic skeleton of pyridonecarboxylic acid are known to be useful synthetic antibacterials for their excellent antibacterial activities and wide antibacterial spectrum. Among such compounds, norfloxacin (Japanese Patent Application Laid-open No. 53-141286), enoxacin (Japanese Patent Application Laid-Open No. 55-31042), ofloxacin (Japanese Patent Application Laid-Open No. 57-46986), ciprofloxacin (Japanese Patent Application Laid-Open No. 58-74667), tosufloxacin (Japanese Patent Application Laid-Open No. 60-228479), and the like are widely used in clinical practice for treating infections.
These compounds, however, need further improvements in antibacterial activities, intestinal absorption, metabolic stability, and side effects, and in particular, in phototoxicity and cytotoxicity.